Summary Stressful experiences in infancy and childhood can disrupt the process of normal development, producing life-long impacts on human health. Such experiences are powerful predictors of later life disease and mortality risk, and exposure to multiple early life stressors can have even more potent effects. These observations suggest that adverse early experiences become biologically embedded in human physiology. However, the molecular mechanisms that mediate the embedding process are not well understood, challenging our ability to predict susceptible individuals and develop effective intervention strategies. The goal of the proposed work is to leverage an emerging model for genomics in natural animal populations to investigate the effects of early life stress on genome-wide DNA methylation levels. DNA methylation is an epigenetic mechanism that is strongly influenced by early life conditions, can remain stable over time, and can influence downstream traits through its effects on gene regulation. However, we still know little about its importance in mediating the effects of early life stressors. Specifically, we do not understand the genes and pathways most affected by early life stress, the degree to which these effects persist over time, or the environmental, behavioral, or genetic factors that mediate inter-individual differences in susceptibility. Part of the challenge in answering these questions lies in the difficulty of collecting environmental data and biological samples for the same individuals and families over time. Animal models provide an opportunity to overcome this challenge. To do so, this proposal takes advantage of an intensively studied primate population, the wild baboons of the Amboseli ecosystem of Kenya, that have been the subjects of longitudinal study for up to 8 contiguous generations. In Amboseli, early life stressors have profound effects on fertility and survival, even in the absence of health risk behaviors like smoking, alcohol consumption, or poor diet. We propose to investigate the epigenetic consequences of these early life stressors on a genome-wide scale. Specifically, we will test the unique and cumulative effects of major early life stressors on DNA methylation levels in blood, investigate the relationship between early adversity- associated differential methylation and gene regulation, and investigate the physiological and behavioral pathways that connect early adversity to the epigenome later in life. We will also test the degree to which the signature of early life effects persists over time, using longitudinally collected repeated samples from individuals and families. Finally, we will investigate whether genotype, behavioral patterns, or environmental conditions affect rates of change, and use Mendelian randomization analyses to dissect the causal pathways that link the early environment to epigenetic patterns. Together, our results will provide an unusually comprehensive window into the relationship between early adversity and the epigenome. They will thus shed new light into the role of epigenetics in mediating the long-term effects of early adversity during development.